Execution Permissions cannot be required error when opening SharePoint Central Administration

Question

The following is the stack trace can anyone share what might be causing and how to resolve this.
Execution permission cannot be acquired.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.Security.Policy.PolicyException: Execution permission cannot be acquired.
Source Error:
An unhandled exception was generated during the execution of the current web request. Information regarding the origin and location of the exception can be identified using the exception stack trace below.  
Stack Trace:
[PolicyException: Execution permission cannot be acquired.]
   System.Security.SecurityManager.ResolvePolicy(Evidence evidence, PermissionSet reqdPset, PermissionSet optPset, PermissionSet denyPset, PermissionSet& denied, Boolean checkExecutionPermission) [phone]
   System.Security.SecurityManager.ResolvePolicy(Evidence evidence, PermissionSet reqdPset, PermissionSet optPset, PermissionSet denyPset, PermissionSet& denied, Int32& securitySpecialFlags, Boolean checkExecutionPermission) +97
[FileLoadException: Could not load file or assembly 'Ajax, Version=5.7.20.2, Culture=neutral, PublicKeyToken=null' or one of its dependencies. Failed to grant permission to execute. (Exception from HRESULT: 0x80131418)]
   System.Reflection.Assembly._nLoad(AssemblyName fileName, String codeBase, Evidence assemblySecurity, Assembly locationHint, StackCrawlMark& stackMark, Boolean throwOnFileNotFound, Boolean forIntrospection) +0
   System.Reflection.Assembly.InternalLoad(AssemblyName assemblyRef, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +416
   System.Reflection.Assembly.InternalLoad(String assemblyString, Evidence assemblySecurity, StackCrawlMark& stackMark, Boolean forIntrospection) +166
   System.Reflection.Assembly.Load(String assemblyString) +35
   System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) +190
[ConfigurationErrorsException: Could not load file or assembly 'Ajax, Version=5.7.20.2, Culture=neutral, PublicKeyToken=null' or one of its dependencies. Failed to grant permission to execute. (Exception from HRESULT: 0x80131418)]
   System.Web.Configuration.CompilationSection.LoadAssemblyHelper(String assemblyName, Boolean starDirective) [phone]
   System.Web.Configuration.CompilationSection.LoadAllAssembliesFromAppDomainBinDirectory() +388
   System.Web.Configuration.CompilationSection.LoadAssembly(AssemblyInfo ai) +232
   System.Web.Configuration.AssemblyInfo.get_AssemblyInternal() +48
   System.Web.Compilation.BuildManager.GetReferencedAssemblies(CompilationSection compConfig) +210
   System.Web.Compilation.BuildProvidersCompiler..ctor(VirtualPath configPath, Boolean supportLocalization, String outputAssemblyName) +76
   System.Web.Compilation.CodeDirectoryCompiler.GetCodeDirectoryAssembly(VirtualPath virtualDir, CodeDirectoryType dirType, String assemblyName, StringSet excludedSubdirectories, Boolean isDirectoryAllowed) [phone]
   System.Web.Compilation.BuildManager.CompileCodeDirectory(VirtualPath virtualDir, CodeDirectoryType dirType, String assemblyName, StringSet excludedSubdirectories) +185
   System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +551
[HttpException (0x80004005): Could not load file or assembly 'Ajax, Version=5.7.20.2, Culture=neutral, PublicKeyToken=null' or one of its dependencies. Failed to grant permission to execute. (Exception from HRESULT: 0x80131418)]
   System.Web.Compilation.BuildManager.ReportTopLevelCompilationException() +76
   System.Web.Compilation.BuildManager.EnsureTopLevelFilesCompiled() +1012
   System.Web.Hosting.HostingEnvironment.Initialize(ApplicationManager appManager, IApplicationHost appHost, IConfigMapPathFactory configMapPathFactory, HostingEnvironmentParameters hostingParameters) +1025
[HttpException (0x80004005): Could not load file or assembly 'Ajax, Version=5.7.20.2, Culture=neutral, PublicKeyToken=null' or one of its dependencies. Failed to grant permission to execute. (Exception from HRESULT: 0x80131418)]
   System.Web.HttpRuntime.FirstRequestInit(HttpContext context) [phone]
   System.Web.HttpRuntime.EnsureFirstRequestInit(HttpContext context) +88
   System.Web.HttpRuntime.ProcessRequestNotificationPrivate(IIS7WorkerRequest wr, HttpContext context) +4405156
 

Answer 1

Hi karabo,
According to your error message, it says that the ajax.dll (Version=5.7.20.2) assembly is missing.
As far as I know, SharePoint Central Administration web application does not refer to the ajax.dll assembly by OOB. 
Do you have any custom solution which reference ajax.dll assembly? If so, please undeploy it before your solution is working fine.
Also you can try to copy the ajax.dll assembly to Global Assembly Cache or your Central Administration web application Bin directory.
Reference:
http://www.herdprotect.com/ajax.dll-fc852aef74018cc802cbcb9b6dbc470799af2885.aspx
https://msdn.microsoft.com/en-us/library/office/ms521365%28v=office.12%29.aspx
Best Regards,
Eric
TechNet Community Support
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